Linear motor

ABSTRACT

A linear motor includes tubular outer yoke ( 4 ), tubular inner yoke ( 3 ) disposed in outer yoke ( 4 ), coil ( 2 ) provided to inner yoke ( 3 ), permanent magnet (5 a , 5 b ) vibrating following a magnetic flux produced by coil ( 2 ), and vibrator ( 6 ) made of magnetic material and supporting permanent magnets (5 a , 5 b ). Magnetic loop produced by outer yoke ( 4 ) and inner yoke ( 3 ) travels through vibrator ( 6 ) free from interference by vibrator ( 6 ) because vibrator ( 6 ) is made of magnetic material. As a result, the linear motor vibrates efficiently.

TECHNICAL FIELD

The present invention relates to a linear motor performing linearmotion.

BACKGROUND ART

FIG. 19 illustrates a conventional linear motor. Tubular outer yoke 201houses tubular inner yoke 203 having coil 202. Permanent magnet 204 isdisposed between outer yoke 201 and inner yoke 203. Magnet 204 vibratesfollowing the magnetic flux generated by inner yoke 203, so that avibrator—fixing magnet 204—reciprocates.

The linear motor discussed above; however, has the following problems:

(1) The permanent magnet is fixed to the vibrator on its outer yokeside. The vibrator is thus positioned between the inner yoke having thecoil and the permanent magnet. Thus a space between the inner yoke andthe magnet becomes too wide. As a result, magnetic-flux-path incurs someloss. Further, the magnetic flux generated by the inner yoke changesgreatly, so that eddy current is produced at a vibrator facing the inneryoke.

(2) The vibrator supporting the permanent magnet is non-magnetic body,thus when the vibrator is placed between the magnet and the yoke,non-magnetic-section other than the space is produced. This structureallows the non-magnetic-section to interfere with magnetic-flux forgenerating vibration, thus the vibrator cannot vibrate efficiently.

(3) Both the inner and outer yokes are formed by laminatingelectromagnetic steel in the circumferential direction, therefore,manufacturing them is a cumbersome work.

The objective of the present invention is to provide a linear motor,where a space between the permanent magnet and the inner yoke isprovided as narrow as possible, the production of eddy current is thusrestrained, and the yoke is easy to manufacture.

SUMMARY OF THE INVENTION

The linear motor of the present invention comprises the followingelements:

(a) a tubular outer yoke;

(b) a tubular inner yoke disposed in the outer yoke;

(c) a coil provided to the outer yoke or the inner yoke;

(d) a permanent magnet vibrating between the outer and inner yokesfollowing the magnetic flux generated by the coil; and

(e) a vibrator supporting the permanent magnet and made of magneticmaterial.

The magnetic-flux-loops produced by the outer and inner yokes travelthrough the vibrator without being hindered by the vibrator. As aresult, the linear motor can vibrate efficiently.

Further, in the linear motor of the present invention, the permanentmagnet is fixed to the vibrator on its coil side, so that the magnet isplaced closer to the yoke on the coil side.

Still further, the linear motor of the present invention includes aplurality of coils in the inner yoke or outer yoke, and a plurality ofpermanent magnets on the side opposite to the coils of the vibrator. Theplurality of permanent magnets arranged in the vibrator's vibratingdirection have unlike polarities adjacently. The vibrator has slitsbetween adjacent magnets, so that leakage flux produced between unlikeadjacent polarities can be prevented.

When the electrical resistance of the vibrator of the present inventionis not less than 100 μΩ.cm, the production of eddy current can berestrained.

The permeability of the vibrator of the present invention is preferablymore than ten times of vacuum permeability.

The vibrator is preferably made of the material mainly comprising ironand chrome.

The vibrator is preferably made of the material including 80-90 wt % ofiron and 10-20 wt % of chrome.

The vibrator is preferably made of the material mainly comprising iron,chrome and aluminum.

The vibrator is preferably made of the material including 75-88 wt % ofiron, 10-20 wt % of chrome and 2-5 wt % of aluminum.

The vibrator is preferably made of the material mainly comprising ironand silicon.

The vibrator is preferably made of the material mainly comprising nickeland iron.

At least one slit is provided on a side of the vibrator, so that theproduction of eddy current is restrained. This slit may be long andnarrow in the vibrator's vibrating direction.

At least one electrically insulated section made of resin is provided ona side of the vibrator, so that the production of eddy current isrestrained.

A compressor of the present invention comprises the following elements:

a linear motor including:

a tubular outer yoke;

a tubular inner yoke disposed in the outer yoke;

a coil provided to the outer yoke or the inner yoke;

a permanent magnet vibrating between the outer and inner yokes followingthe magnetic flux generated by the coil; and

a vibrator supporting the permanent magnet and made of magneticmaterial.

The compressor can be driven efficiently.

The linear motor of the present invention comprises the followingelements:

(a) a tubular outer yoke;

(b) a tubular inner yoke disposed in the outer yoke;

(c) a coil provided to the outer yoke or the inner yoke;

(d) a permanent magnet vibrating between the outer and inner yokesfollowing the magnetic flux generated by the coil; and

(e) a vibrator supporting the permanent magnet.

The permanent magnet is fixed to the outer yoke or inner yoke whicheverincludes the coil. This structure allows the permanent magnet to beplaced closer to the yoke having the coil.

The compressor of the present invention comprises the followingelements:

a linear motor including:

a tubular outer yoke;

a tubular inner yoke disposed in the outer yoke;

a coil provided to the outer yoke or the inner yoke;

a permanent magnet vibrating between the outer and inner yokes followingthe magnetic flux generated by the coil; and

a vibrator supporting the permanent magnet.

The permanent magnet is fixed to the outer yoke or inner yoke whicheverincludes the coil. This structure allows the compressor to be drivenefficiently.

The linear motor of the present invention comprises the followingelements:

(a) a yoke formed of compression-formed body made of metal magneticparticles;

(b) a mover vibrating along the yoke.

This structure allows the linear motor to be manufactured with ease.

The linear motor of the present invention may comprise the followingelements:

(a) a tubular outer yoke;

(b) a tubular inner yoke disposed in the outer yoke;

(c) a coil provided to the outer yoke or the inner yoke;

(d) a permanent magnet vibrating between the outer and inner yokesfollowing the magnetic flux generated by the coil; and

(e) a vibrator supporting the permanent magnet.

At least one of the outer yoke or inner yoke may be formed bycompression-formed body made of metal magnetic particles.

The yoke of the compressed and molded body of the present invention maybe made of metal magnetic particles and electrically insulated resin.

The yoke of the linear motor of the present invention may be acompression-formed body made of metal magnetic particles having aninsulated layer on its surface.

The yoke of the linear motor of the present invention is formed by metalmagnetic particles and its surface electrically insulated may be made ofinorganic material.

The yoke of the linear motor of the present invention is divided in thecirumferential direction, so that the production of eddy current isrestrained.

The yoke of the linear motor of the present invention is divided in thecircumferential direction and an insulating layer is provided to thebonding face of the yoke. This structure allows the motor to furtherrestrain the production of eddy current.

The compressor of the present invention comprises a linear motorincluding a yoke formed of a compression-formed body made of metalmagnetic particles and a mover moving along the yoke.

The linear motor of the present invention comprises the followingelements:

(a) a tubular outer yoke;

(b) a tubular inner yoke disposed in the outer yoke;

(c) a coil provided to the outer yoke or the inner yoke;

(d) a permanent magnet vibrating between the outer and inner yokesfollowing the magnetic flux generated by the coil; and

(e) a vibrator supporting the permanent magnet.

At least one of the outer yoke or inner yoke is formed by arranging aplurality of laminated blocks in an annular shape, and a space betweenthe adjacent blocks is formed by the compression-formed body.

The compressor of the present invention comprises the followingelements:

a linear motor including:

(a) a tubular outer yoke;

(b) a tubular inner yoke disposed in the outer yoke;

(c) a coil provided to the outer yoke or the inner yoke;

(d) a permanent magnet vibrating between the outer and inner yokesfollowing the magnetic flux generated by the coil; and

(e) a vibrator supporting the permanent magnet.

At least one of the outer yoke or inner yoke is formed by arranging aplurality of laminated blocks in an annular shape, and a space betweenthe adjacent blocks is formed by the compression-formed body.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) and FIG. 1(b) are a cross section and a plan view of a linearmotor in accordance with a first exemplary embodiment.

FIG. 2(a) is a partial cross section of the linear motor in accordancewith the first embodiment, and FIG. 2(b) is a partial cross section of aconventional linear motor.

FIG. 3(a) and FIG. 3(b) are a cross section and a plan view of a linearmotor in accordance with a second exemplary embodiment.

FIG. 4(a) and FIG. 4(b) are a cross section and a plan view of a linearmotor in accordance with a third exemplary embodiment.

FIG. 5 is a cross section of another linear motor in accordance with thethird embodiment.

FIG. 6(a) and FIG. 6(b) are a cross section and a plan view of a linearmotor in accordance with a fourth exemplary embodiment.

FIG. 7(a) and FIG. 7(b) are a cross section and a plan view of avibrator in accordance with a fourth exemplary embodiment.

FIG. 8 is a cross section of a linear motor in accordance with a fifthexemplary embodiment.

FIG. 9 is a cross section of a vibrator in accordance with the fifthembodiment.

FIG. 10 is a cross section of another vibrator in accordance with thefifth embodiment.

FIG. 11 is a cross section of still another vibrator in accordance withthe fifth embodiment.

FIG. 12 is a cross section of still further another vibrator inaccordance with the fifth embodiment.

FIG. 13(a) and FIG. 13(b) are a cross section and a plan view of alinear motor in accordance with a sixth exemplary embodiment.

FIG. 14 is a flowchart illustrating a manufacturing process of acompressed and molded body in accordance with the sixth embodiment.

FIG. 15 is a flowchart illustrating a manufacturing process of acompression-formed body in accordance with the sixth embodiment.

FIG. 16(a) and FIG. 16(b) are a cross section and a plan view of alinear motor in accordance with a seventh exemplary embodiment.

FIG. 17(a) and FIG. 17(b) are a cross section and a plan view of alinear motor in accordance with an eighth exemplary embodiment.

FIG. 18 is a cross section of a linear motor compressor.

FIG. 19 is a cross section of a conventional linear motor.

BEST MODE FOR CARRYING OUT THE PRESENT INVENTION

(Exemplary Embodiment 1)

FIG. 1 shows a construction of a linear motor. Linear motor 1 comprisesthe following elements:

(a) tubular inner yoke 3;

(b) coils 2 formed by windings wound on inner yoke 3;

(c) outer yoke 4 in which inner yoke 3 is disposed;

(d) permanent magnets 5 a, 5 b situated in a space between inner yoke 3and outer yoke 4, and vibrating following the magnetic flux generated bycoils 2; and

(e) tubular vibrator 6 supporting magnets 5 a, 5 b.

Magnets 5 a, 5 b are fixed to a side face of vibrator 6 on the side ofinner yoke 4. Output section 7, for supplying the vibration of vibrator6 to outside, is disposed at an end of vibrator 6. Output section 7shapes in a lid closing tubular vibrator 6. A resonance spring isdisposed on an output shaft of output section 7. Utilizing the resonanceof the spring saves some force necessary for vibration, and also savessome driving current running through coils 2.

Next, this linear motor is detailed. Inner yoke 3 is formed bylaminating magnetic and rectangular steel sheets having two recesses incircumferential direction, and forms a tubular shape. Successiverecesses form ring-shaped grooves on the outer wall of inner yoke 3.Windings wound on these ring-shaped grooves form coils 2.

Outer yoke 4 is formed by laminating magnetic and rectangular sheets incircumferential direction, and forms a tubular shape. Inner yoke 3 isdisposed in outer yoke 4. The inner wall of outer yoke 4 is parallel tothe outer wall of inner yoke 3, and there is an even clearancetherebetween.

Ring-shaped permanent magnets 5 a, 5 b are bonded or press-fitted to theinner wall of vibrator 6. The magnetic fluxes of magnets 5 a, 5 b aredirected in radial direction of inner yoke 3, and adjacent magnets 5 a,5 b have unlike polarities. The magnet flux of magnet 5 a travels frominner yoke 3 to outer yoke 4, while that of magnet 5 b travels fromouter yoke 4 to inner yoke 3.

The structure discussed above allows the linear motor to vibratevibrator 6 by switching the current of coils 2. When current runsthrough coils 2, outer yoke 4 and inner yoke 3 form magnetic-flux-loops.These loops cause magnetic fluxes to appear at the space, and permanentmagnet 5 moves to approach the magnetic fluxes. Switching the directionof current reverses the magnetic fluxes traveling through the space. Assuch, switching the current-direction vibrates the vibrator.

A first feature of this first embodiment is that magnet 5 a, 5 b arefixed to the vibrator 6 on its inner yoke side, and the linear motor canbe assembled by using magnets 5 a, 5 b in a state of being close toinner yoke 3.

FIG. 2(a) is a partial cross section of the linear motor in accordancewith the first embodiment, and FIG. 2(b) is a partial cross section of aconventional linear motor.

Magnetic-flux for generating vibration is produced in inner yoke 3,therefore, permanent magnet 5, corresponding to the magnetic-fluxes, ispreferably placed as close as possible to inner yoke 3. In thisembodiment, magnet 5 is fixed to vibrator 6 on its inner yoke side.Therefore between magnets 5 a, 5 b and the inner yoke, there is nothingbut a space. Thus magnets 5 a, 5 b can be placed as close as possible toinner yoke 3 including coils 2.

FIG. 2(b) shows that permanent magnet 205, as disclosed in JapaneseExamined Patent H06-91727, is fixed to vibrator 206 on its yoke 204side. The vibrator of the conventional linear motor is made ofnon-magnetic material. As such, magnet 205 is fixed to vibrator 206, andbetween inner yoke 203 having a coils and permanent magnet 205, thereare a space and vibrator 206. Thus the space between magnet 205 andinner yoke 203 is greater than that shown in FIG. 2(a) by the thicknessof vibrator 206. In other words, the conventional magnetic flux producedin inner yoke 203 and affecting magnet 205 is smaller than that in thefirst embodiment.

In this embodiment, permanent magnet 5 is fixed to vibrator 6 on itsinner yoke side 3. This structure allows the motor of the presentinvention to use magnetic-fluxes for generating vibration produced bythe inner yoke more efficiently than the conventional motor. Thisstructure also allows the vibrator to be placed more distantly from theinner yoke, which produces the magnetic-fluxes for generating vibration,than the conventional case, thereby restraining the production of eddycurrent.

The vibrator of the first embodiment is made of magnetic material;however, the vibrator may be made of non-magnetic material with the sameadvantage.

A second feature of the first embodiment is that vibrator 6 which fixesmagnets 5 a, 5 b has magnetism. Since the conventional vibrator is madeof non-magnetic material, which hinders the magnetic fluxes of themagnetic loops formed between inner yoke 3 and outer yoke 4. However,vibrator 6, in this embodiment, is made of magnetic material and doesnot hinder the magnetic loops produced between inner yoke 3 and outeryoke 4. In other words, because vibrator 6 is made of magnetic material,non-magnetic distance between outer yoke 4 and inner yoke 3 can bepractically shortened.

Magnets 5 a, 5 b are fixed to vibrator 6 on its inner yoke 3 side, sothat vibrator 6 can be utilized as a back yoke of magnets 5 a, 5 b. Aplurality of permanent magnets 5 a, 5 b are fixed to a common vibrator,and magnets 5 a, 5 b are magnetically coupled with each other byvibrator 6. In other words, vibrator 6 functions as the back yoke andthus uses the greater magnetic fluxes of magnets 5 a, 5 b.

Vibrator 6 has magnetism and comprises iron, chrome and aluminum. Italso includes silicon not more than 3 wt % for adjusting its resistancevalue. To be more specific about ingredients, the material includes75-88 wt % of iron, 10-20 wt % of chrome, and 2-5 wt % of aluminum.Vibrator's permeability is more than 10 times as much as that of vacuum.

This structure discussed above allows outer yoke 4 and inner yoke 3 tobe spaced with a shorter magnetic gap, and thus they reciprocateefficiently.

Further, vibrator 6 is placed between outer yoke 4 and permanent magnets5 a, 5 b, so that vibrator 6 is utilized as the back yoke.

(Exemplary Embodiment 2)

Linear motor 21 shown in FIG. 3 comprises the following elements:

(a) tubular outer yoke 23 having coils 22 where windings are coiled;

(b) tubular inner yoke 24 disposed inside the outer yoke;

(c) permanent magnets 25 a, 25 b placed in a space between outer andinner yokes 23, 24 and vibrating following the magnetic fluxes generatedby coils 22; and

(d) vibrator 26 supporting and fixing the permanent magnets 25 a, 25 b.vibrator 26, fixing magnets 25 a, 25 b, is placed between magnets 25 a,25 b and inner yoke 24, and has magnetism. Inner yoke 24 and outer yoke23 are made by laminating electromagnetic steel sheets incircumferential direction.

The structure discussed above allows the space between outer yoke 23 andinner yoke 24 to be magnetically shortened and thus they reciprocateefficiently. Further, vibrator 26 is placed between inner yoke 24 andpermanent magnets 25 a, 25 b, so that vibrator 26 is utilized as a backyoke.

As shown in FIG. 18, when the linear motor in accordance with the secondembodiment is incorporated into a compressor, highly efficient drivingcan be expected. Linear compressor 150 comprises linear motor 160,discharge mechanism 170, spring mechanism 171, sealed container 172 andsupporting mechanism 173.

(Exemplary Embodiment 3)

FIG. 4 shows a construction of linear motor 31, which comprises thefollowing elements:

(a) tubular inner yoke 33;

(b) coil 32 of which windings are coiled on inner yoke 33;

(c) outer yoke 34 having inner yoke 33 therein;

(d) permanent magnet 35 disposed in a space between inner yoke 33 andouter yoke 34, and vibrating following the magnetic flux produced bycoil 32; and

(e) tubular vibrator 36 supporting magnet 35.

Permanent magnet 35 is fixed to vibrator 36 on its inner yoke 33 side.On one end of vibrator 36, there is output section 37 for supplying thevibration of vibrator 36 to outside. Output section 37 shapes in as ifit closes tubular vibrator 36.

This linear motor is detailed hereinafter. Tubular inner yoke 33 is madeby laminating rectangular electromagnetic steel sheets having a recessin circumferential direction. The successive recess forms a ring-shapedgroove on outside of inner yoke 33. Winding wires on this groove formscoil 32.

The structure discussed above magnetically shortens the space betweenouter yoke 34 and inner yoke 33 even if linear motor 31 includes onlyone coil 32. Thus efficient reciprocating motion can be expected.Further, vibrator 36 is placed between outer yoke 34 and permanentmagnets 35, so that vibrator 36 is utilized as a back yoke.

As shown in FIG. 5, even one coil 42 placed on outer yoke 44 wouldproduce the same advantage.

(Exemplary Embodiment 4)

Linear motor 51 shown in FIG. 6 comprises the following elements:

(a) tubular inner yoke 53 having coils 52 where wires are wound;

(b) outer yoke 54 inside which inner yoke 53 is placed;

(c) ring-shaped permanent magnets 55 a, 55 b vibrating within a spacebetween inner yoke 53 and outer yoke 54 following the magnetic fluxesproduced by coils 52; and

(d) vibrator 56 supporting magnets 55 a, 55 b and is made of magneticmaterial.

A feature of this fourth embodiment is that vibrator 56 has slit 59between magnets 55 a and 55 b as FIG. 7 shows. Slit 59 is formedextendedly along the circumference direction of vibrator 56.

The magnetic fluxes produced by inner yoke 53 forms, via vibrator 56,magnetic loops between outer yoke 54 and inner yoke 53. Vibrator 56 issituated between magnets 55 a, 55 b and inner yoke 53; however sincevibrator 56 is made of magnetic material, the thickness of vibrator 56is not included in magnetic distance. This structure, i.e. permanentmagnets 55 a, 55 b are fixed on outer wall of vibrator 56, makes themanufacturing with ease because permanent magnets can be mounted to thevibrator on its outer wall.

If magnets 55 a, 55 b are only pasted to vibrator 56, leakage flux isproduced between magnets 55 a and 55 b using vibrator 56 as amagnetic-flux-path. Therefore, as shown in FIG. 7, slits 59 are providedbetween magnets 55 a and 55 b in order to reduce the leakage flux.

(Exemplary Embodiment 5)

Linear motor 61 shown in FIG. 8 comprises the following elements:

(a) tubular inner yoke 63 having coils 62 where wires are wound;

(b) outer yoke 64 inside which inner yoke 63 is placed;

(c) ring-shaped permanent magnets 65 a, 65 b vibrating within a spacebetween inner yoke 63 and outer yoke 64 following the magnetic fluxesproduced by coils 62; and

(d) vibrator 66 supporting magnets 65 a, 65 b and is made of magneticmaterial.

Ring-shaped permanent magnets 65 a, 65 b are fixedly bonded orpress-fitted on the inner wall of vibrator 66. The magnetic fluxes ofmagnets 65 a, 65 b are directed in radial direction of inner yoke 63,and adjacent magnets 65 have unlike polarities. Magnetic flux of magnet65 a travels from inner yoke 63 to outer yoke 64 while that of magnet 65b travels from outer yoke 64 to inner yoke 63.

This structure allows the linear motor to vibrate vibrator 66 byswitching the current at coils 62. When current runs through coils 62,magnetic loops are formed between outer yoke 64 and inner yoke 63. Thismagnetic loops cause magnetic fluxes to appear in the space between theinner yoke and outer yoke, and permanent magnet 65 approaches thismagnetic flux. Then switching the current reverses the magnetic fluxestraveling through the space, and magnet 65 moves in accordance with themagnetic fluxes. As such, vibrator 66 is vibrated by switching thecurrent direction.

The feature of this fifth embodiment is that long and narrow slits 67are provided in the vibrating direction. Vibrator 66 vibrates crossingthe magnetic fluxes, therefore, eddy current tends to appear in thecircumferential direction of tubular vibrator 66. Slits 67 are thusprovided in the vibrating direction of vibrator 66 so that theproduction of eddy current in the circumferential direction can berestrained.

The shape of the slits may be checked pattern 71 or zigzag pattern 72 asshown in FIGS. 10 and 11 in order to reinforce the strength of vibrator66.

Instead of the slits, long and narrow electrical insulating sections 73made of resin may be provided along the vibrating direction of thevibrator as shown in FIG. 12. Vibrator 66 shown in FIG. 12 is formed byarranging a plurality of rectangular magnetic plates in an annular shapeand respective plates are bonded with resin material.

(Exemplary Embodiment 6)

Linear motor 81 shown in FIG. 13 comprises the following elements:

(a) tubular inner yoke 83 having coils 82 where wires are wound;

(b) outer yoke 84 inside which inner yoke 83 is placed;

(c) permanent magnets 85 a, 85 b vibrating within a space between inneryoke 83 and outer yoke 84 following the magnetic fluxes produced bycoils 82; and

(d) tubular vibrator 86 supporting magnets 85 a, 85 b and being made ofmagnetic material.

Permanent magnets 85 a, 85 b are fixed to vibrator 86 on its inner yoke83 side. On one end of vibrator 86, there is output section 87 fortaking out vibration of vibrator 86. Output section 87 shapes in as ifit closes tubular vibrator 86.

Inner yoke 83 and outer yoke 84, features of this sixth embodiment, aremade by compressing and molding the mixture of metal magnetic particlesand electrically insulating resin. The adjacent metal magnetic particlesin this compressed and molded body are electrically insulated by theinsulating resin, therefore, the production of eddy current loss can berestrained without laminating electromagnetic steel sheets incircumferential direction. The yokes thus can eliminate the laminate.

Next, a manufacturing method of inner yoke 83 and outer yoke 84 isdescribed hereinafter with reference to FIG. 14.

The metal magnetic particles used for sintered cores for the linearmotor comprises mainly iron; however, it is not limited to iron, and itmay comprise an alloy of iron and silicon, or iron and aluminum, ironand nickel, iron and cobalt alloy, nickel and iron, or an alloy ofnickel and iron including chrome, aluminum, and titanium. The materialmay be a mixture of these alloys.

One of these metal magnetic particles and electrically insulating resin,e.g. epoxy resin, nylon resin, polymide resin, polyamide resin,polyester resin, are mixed.

The metal magnetic particles mixed with the insulating resin is chargedinto a mold of the desired core for the linear motor, and compressionmolding not more than 1000 MPa is carried out to produce a shape ofcore. After this, thermal process not more than 300° C. is carried outfor hardening the resin.

As such, the yoke of the linear motor can be unitarily manufactured. Ayoke of a conventional linear motor has been produced by laminating aplurality of electromagnetic steel sheets in circumference direction,therefore, it is difficult to manufacture this yoke from the mechanicalstandpoint. This new manufacturing method eliminates the laminate ofelectromagnetic steel sheets, and yet obtains the same advantage, i.e.restraining the production of eddy current, as the laminated yoke.

Another factor of restraining the production of eddy current is that theadjacent metal-magnetic-particles are electrically insulated. Theelectrically insulating resin functions also as a binder forfusion-splicing the metal magnetic particles.

The manufacturing method of the compressed and molded body, i.e.compressing the particles and resin to be molded, is discussed above;however, as shown in FIG. 15, metal magnetic particles on which surfacean electrically insulating layer is disposed can be compression-formed.

The metal magnetic particles used for sintered cores for the linearmotor comprises mainly iron; however, it is not limited to iron, and itmay comprise an alloy of iron and silicon, or iron and aluminum, ironand nickel, iron and cobalt alloy. The material may be a mixture ofthese alloys. An electrically insulating layer made of e.g. inorganicmaterial such as phosphate is formed on the surface of these particles.This layer insulates the adjacent metal magnetic particles, so that theproduction of eddy current is restrained.

The metal magnetic particles having electrical insulation on theirsurfaces are charged in a mold, and compression forming not more than1000 MPa is carried out to produce a shape of core. After this, thermalprocess at 350-800° C. is carried out for improving magneticcharacteristics such as lowering hysteresis loss.

(Exemplary Embodiment 7)

Linear motor 91 shown in FIG. 16 comprises the following elements:

(a) tubular inner yoke 93 having coil 92 where wires are wound;

(b) outer yoke 94 inside which inner yoke 93 is placed;

(c) permanent magnets 95 vibrating within a space between inner yoke 93and outer yoke 94 following the magnetic fluxes produced by coil 92; and

(d) tubular vibrator 96 supporting magnets 95 and is made of magneticmaterial.

Permanent magnets 95 is fixed to vibrator 96 on its inner yoke 93 side.On one end of vibrator 96, there is output section 97 for taking outvibration of vibrator 96. Output section 97 shapes in as if it closestubular vibrator 96.

Inner yoke 93 and outer yoke 94 are made by compressing and molding themixture of metal magnetic particles and electrically insulating resin.

The features of this seventh embodiment are that inner yoke 93 and outeryoke 94 are compressed and molded bodies, and they are divided into aplurality of blocks in the circumference direction, and insulatinglayers 98 are provided to the divided bonding faces of the yoke.

As such, the yoke is divided into pieces, they can be manufactured withsmaller molds, and thus the manufacturing cost can be lowered. Further,if the yoke is divided in the circumferential direction, and insulatinglayers 98 are provided on bonding faces, the production of eddy currentis further lowered.

(Exemplary Embodiment 8)

Linear motor 101 shown in FIG. 17 comprises the following elements:

(a) tubular inner yoke 103 having coils 102 where wires are wound;

(b) outer yoke 104 inside which inner yoke 103 is placed;

(c) permanent magnets 105 vibrating within a space between inner yoke103 and outer yoke 104 following the magnetic fluxes produced by coils102; and

(d) tubular vibrator 106 supporting magnets 105 and is made of magneticmaterial.

A feature of this eighth embodiment is that inside yoke 103 and outeryoke 104, both are compressed and molded bodies, are formed by combiningmulti-layered blocks 110 made by laminating electromagnetic steel sheetswith compressed and molded body 111 made by compressing and molding themetal magnetic particles and an electrical insulating resin.

As shown in FIG. 17, multi-layered blocks 110 are arranged incircumference shape, and compressed and molded bodies 111 fit into gapsbetween the adjacent blocks are combined with blocks 110, therebyobtaining inner yoke 103 and outer yoke 104.

Further, a number of multi-layered blocks is increased, and compressedand molded bodies 111 are disposed therebetween. One plate ofelectromagnetic steel may be treated as a multi-layered block, andcompressed and molded bodies are disposed between the adjacent plates.This structure is still within the scope of the present invention.

Industrial Applicability

A vibrator is made of magnetic material, so that a space is shortened.As a result, a highly efficient linear motor is provided.

Further, a permanent magnet is fixed to the vibrator on its coil side,thereby shortening the space between a yoke on a coil-side and thepermanent magnet.

Still further, a yoke can be manufactured with ease.

What is claimed is:
 1. A linear motor comprising: (a) a tubular outeryoke; (b) a tubular inner yoke disposed in said outer yoke; (c) a coilprovided to one of said outer yoke and said inner yoke; (d) a permanentmagnet located between said outer yoke and said inner yoke and thatvibrates in response to a magnetic flux produced by said coil; and (e) avibrator supporting said permanent magnet, wherein at least one of saidouter yoke and said inner yoke is formed by arranging a plurality ofmulti-layered blocks in an annular shape, with a spacing betweenadjacent blocks thereof filled with a compression-formed body.
 2. Acompressor including a linear motor, said motor comprising: (a) atubular outer yoke; (b) a tubular inner yoke disposed in said outeryoke; (c) a coil provided to one of said outer yoke and said inner yoke;(d) a permanent magnet located between said outer yoke and said inneryoke and that vibrates in response to a magnetic flux produced by saidcoil; and (e) a vibrator supporting said permanent magnet, wherein atleast one of said outer yoke and said inner yoke is formed by arranginga plurality of multi-layered blocks in an annular shape, with a spacingbetween adjacent blocks thereof filled with a compression-formed body.